My invention pertains to a power varistor circuit arrangement for use in railroad signaling systems. More specifically, the invention relates to a vital varistor circuit arrangement usable as a track relay means in alternating current track circuits on electrified railroads.
As a matter of economy and efficiency, electrified railroads in the United States are planning to change to commercial 60 Hz propulsion power sources to replace the long used 25 Hz propulsion power generated by special apparatus at privately owned generating stations. Any new electrification will also be at the commercial power frequency. The signaling systems in such electrified railroads have for many years used 100 Hz alternating current (A.C.) track circuits including centrifugal type track relays which are effectively two winding, dual input, synchronous motor or detector devices designed to be immune to the 25 Hz propulsion current flowing in the rails. One winding of the relay is energized direct from the track circuit power source. The second winding receives energy through the section rails from the same track circuit source connected at the other end. The relay operates to indicate an unoccupied track section only when both windings are energized by track circuit frequency currents having a phase angle relationship within predetermined limits. It is impractical, in the process of changing propulsion frequency, to also change out the existing 100 Hz track circuits. However, the present centrifugal relays are not sufficiently immune to the 60 Hz frequency to assure no response by the relays to propulsion currents of the new frequency flowing in the rails. In addition, centrifugal relays inherently require considerable and frequent preventative maintenance to assure proper and reliable operation. Therefore, it is desirable, actually required to substitute a passive network not responsive to 60 Hz currents which will permit continued use of the 100 Hz track circuits but with conventional, vital direct current (D.C.) track relays which will not respond to, that is, which are immunized from, propulsion currents whether of the 25 or 60 Hz frequency.
Accordingly, an object of my invention is a passive circuit network for controlling a vital relay which serves as the track relay for alternating current track circuits in electrified railroads.
Also an object of my invention is a vital power varistor detector circuit arrangement responsive only to dual input signals of the same preselected frequency and within a predetermined phase relationship.
Another object of the invention is a varistor circuit arrangement to replace frequency and phase responsive track relays in vital, alternating current railroad track circuits.
A further object of my invention is an improved frequency selective track relay means for alternating current track circuits in electrified railroads.
Still another object of the invention is a track circuit arrangement for electrified railroads including a tuned varistor circuit network at the receiving end for energizing a vital track relay only in response to received energy of the preselected track circuit frequency.
Also an object of the invention is a synchronous detector circuit network including a varistor which replaces the centrifugal track relay in alternating current track circuits for electrified railroads.
A still further object of my invention is a varistor circuit network responsive to inputs from two phase related sources having the same preselected frequency for producing a registerable output signal only if both inputs are present, are of the same frequency, and are within a predetermined phase relationship.
It is also an object of the invention to supply, for an electrified railroad track section using impedance bonds for the propulsion power return, an alternating current track circuit which includes a source of alternating current energy, having a frequency different from that of the propulsion power, connected across the rails at one end and a train detector means having a first input coupled to the track circuit source and a second tuned input coupled across the rails at the other end of that section, the input signals being processed in a circuit network including a tuned filter path and a varistor device to energize a vital track relay to register an unoccupied track section only if both input signals of the track circuit frequency are received and are within a predetermined phase relationship.
Other objects, features, and advantages of the invention will become apparent from the following specification and appended claims when taken in connection with the accompanying drawings.